Blu-ray disc is next generation optical disc storage medium. The name Blu-ray Disc is derived from the blue-violet laser used to read the disc. Unlike the normal DVD which uses 650 nanometer wavelength red lasers, it uses 400 nanometer blue violet lasers to read and write. The disc was jointly developed by Blu-ray Disc Association, a group of the world's leading consumer electronics, personal computer and media manufacturers (including Apple, Dell, Hitachi, HP, JVC, LG, Mitsubishi, Panasonic, Pioneer, Philips, Samsung, Sharp, Sony, TDK and Thomson).
In 1998 when High Definition Televisions were introduced, there was no specific way to record and play the high definition (HD) videos. Even the storage capacity of normal DVD's was about 4.7GB. A lot of space was required to store high definition codecs on a single medium. It was understood that if shorter wavelength lasers were utilized then optical storage could increase. It was a remarkable achievement in laser technology when the first blue laser diode was invented by Shuji Nakamura.
Sony started two projects applying the new diodes: Ultra Density Optical (UDO) and DVR Blue, together with Pioneer, a format of rewritable discs that would eventually become Blu-ray Disc specifically BD-RE. The technology of these formats is same. The first DVR Blue prototypes were unveiled at the CEATEC exhibition in October 2000. On February 19, 2002, the project was officially announced as Blu-ray, and Blu-ray Disc Founders was founded by the nine initial members. The first consumer device was in stores on April 10, 2003. This device was the Sony BDZ-S77, a BD-RE recorder that was made available only in Japan. The recommended price at that time was US$3800.
A single layer Blu-ray disc has a capacity of 25GB, about 5 times normal DVD. It can store high definition content like audio and video on a single media. It can also hold photos, data and other digital content.
Design and operation:
All the digital data stored in disc is in the form of pits and lands (normally represents ones and zeros, the NRZI scheme). Pits are normally spiral grooves that run from the center of the disc to its edges. Other side of these pits contains bubbles. Laser reads these bubbles in order to run the program stored in DVD. These pits must be smaller and closely packed so that more data is stored on the disc. Unlike current DVDs, which use a red laser to read and write data, Blu-ray uses a blue laser. A blue laser has a shorter wavelength (405 nanometers) than a red laser (650 nanometers). The smaller beam focuses more precisely, enabling it to read information recorded in pits that are only 0.15 microns (m) long, this is more than twice as small as the pits on a DVD. Blu-ray has reduced the track pitch from 0.74 microns to 0.32 microns. The smaller pits, smaller beam and shorter track pitch together enable a single-layer Blu-ray disc to hold more than 25 GB of information, which is about five times of the amount of information that can be stored on a typical DVD.
Each Blu-ray disc is about the same thickness (1.2 millimeters) as a DVD. But the data storage methods are different in two types of discs. In a DVD, the data is sandwiched between two polycarbonate layers, each 0.6-mm thick. Having a polycarbonate layer on top of the data can cause a problem called birefringence, in which the substrate layer refracts the laser light into two separate beams. If the beam is split too widely, the disc cannot be read. Also, if the DVD surface is not exactly flat, and is therefore not exactly perpendicular to the beam, it can lead to a problem known as disc tilt, in which the laser beam is distorted. All of these issues lead to a very involved manufacturing process.
The design of the Blu-ray discs saves on manufacturing costs. Traditional DVDs are built by injection molding the two 0.6-mm discs between which the recording layer is sandwiched. The process must be done very carefully to prevent birefringence.
- The two discs are molded.
- The recording layer is added to one of the discs.
- The two discs are glued together.
Blu-ray discs only do the injection-molding process on a single 1.1-mm disc instead of two separate discs, which reduces cost. By doing this initial cost is saved and it also cover up the cost of adding the protective layer, so the final price is no more than the price of a regular DVD.
Read and Write Operation:
The Blu-ray disc overcomes DVD-reading issues by storing the data on top of a 1.1-mm-thick polycarbonate layer. Having the data on top prevents birefringence and therefore prevents readability problems. And, with the recording layer sitting closer to the objective lens of the reading mechanism, the problem of disc tilt is virtually eliminated. Because the data is closer to the surface, a hard coating is placed on the outside of the disc to protect it from scratches and fingerprints.
Dual layer Disc
Dual Layer Blu-ray disc contains two layers for recording, having twice the capacity. The two layers L0 and L1 are separated by a spacer. The thickness of the spacer depends upon amount of stray light. The laser beam directly falls on layer L0 while layer L1 receives fraction of light transmitted through L0. These layers must have same reflection and equal sensitivity. Therefore the first stack is made transparent by using a minimum of 10nm thin Ag mirror and thin phase change layer. Whereas layer L1 is designed as similar to that of a single layer discs. Normally a protective cover is placed above L0 in order to prevent any defects or scratches.
Blu-ray discs offer a new level of interactivity in addition to large storage capacity than traditional DVDs. With Blu-ray, you can:
- Record high-definition television (HDTV) without any quality loss.
- Instantly skip to any spot on the disc.
- Record one program while watching another on the disc and create playlist.
- edit or reorder programs recorded on the disc
- Automatically search for an empty space on the disc to avoid recording over a program.
- Access the Web to download subtitles and other extra features.
- Record an outstanding 25GB of data on a single-sided RW disc. That's equivalent to 5 standard DVDs on one disc. Imagine over 4 hours of High Definition Television or over 11 hours of Standard Definition.
Next Generation variances:
Progress is being made by different organization to reduce the cost of BD. On April 2004 Sony and Toppan Printing announced the successful development of BD that is 51% composed of paper, which could reduce production cost and improves its environmental friendliness. A research reveals 150 GB, 6-Layer Write Once Disc for Blu-ray Disc System, “We achieved the optimum recording powers and the jitter values less than 160 mW and 8.0% for each layer at the user data recording rate of 72 Mbps.”
(Mishima, K.; Yoshitoku, D.; Itoh, H.; Yamatsu, S.; Inoue, H.; Komaki, T.; Tanaka, K.; Aoi, T.)
Blu-ray disc is a high definition optical storage disc format developed by Blu-ray Disc Association. BD can store video and audio in a very high quality making it much more advanced than ordinary CD's or DVD's. Shorter wavelength blue-violet laser allows storing more bits then red lasers therefore enhancing the capacity of the disc. The all credit of Blu Ray technology goes to the inventor of the blue LED Dr.Shuji Nakamura of Nichia Corporation. That LED was mainly composed of material called InGaN.
With the Advances Access Content System, Blu-ray Disc is capable of providing extra encryption to High Definition content. This is current need of the industry because hackers around the world are a big threat to organization that provides such content like movies or games. Blu-ray disc is scratch less media disc making it more reliable than ordinary discs. Modern requirement needs faster access to data, BD provides faster way to store and access data. The Blu-ray disc has the data placed on top of a 1.1-mm-thick polycarbonate layer. Having the data on top prevents birefringence and therefore prevents readability problems. At present due to its construction and manufacturing process the initial cost is less then than it old models. The Data rate and storage space is much higher than the simple optical Cds. Now a days we have 2 layer Blu-Ray disc which have a capacity of 25 Gb per layer and data rate in range of 36 - 70 Mbps. Almost all over the world many renown companies are manufacturing Blu Ray discs which are widely available in the world with different color codes as:
A/1: The Americas, and their dependencies, East Asia (except Mainland China and Mongolia), Southeast Asia.
B/2: Africa, Southwest Asia, Europe (except Belarus, Russia and Ukraine), Oceania, and their dependencies.
C/3: Central Asia, East Asia (Mainland China and Mongolia only), South Asia, central Eurasia (including Russia), and their dependencies.
Sources and References:
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- “Blu-ray Disc to Deliver Five Times Disc Capacity of DVD Discs with Comparable Costs Per Disc.” BDF Press Release. Blu-ray Disc, March 29, 2004.
- Blu-ray FAQ, Blu-ray.com
- Frauenheim, Ed. Standards Battle Could Shoot Both Sides in Foot, CNET news.com, August 17, 2004.
- Labriola, Don. “Blue Lasers Boost DVD Capacity,” PC Magazine, August 3, 2004, page 30.
- Large Capacity Optical Disc Video Recording Format “Blu-ray” Disc” Established, Blu-ray Disc Press Release, February 19, 2002.
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- blu-ray wikipedia
- Circuit Design and Noise Considerations for
- Future Blu-ray Disc Optical Storage Technology
- Blu ray selling shops